1. Field of the Invention
The present invention generally relates to a torque converter which includes a pump wheel driven by an internal combustion engine, a turbine wheel coupled to a drive shaft, and a stator which can be blocked in one direction of rotation, all of which together form a converter circuit filled with hydraulic fluid, preferably oil. The torque converter further includes a lock-up clutch which is located axially between the outside of the turbine wheel and the facing inner side of the converter housing which forms the connection between the pump wheel and the internal combustion engine. The torque converter also includes a piston which, like the converter housing, can also be driven preferably with some slip with respect to the corresponding friction lining. The piston can be displaced axially and, with the converter housing, defines a chamber. The piston can be brought into contact, by means of a first friction lining, with a plate which is non-rotationally fastened to the turbine wheel, which plate is engaged, for its part, with its other side by means of a second friction lining with the converter housing.
2. Background Information
Such a torque converter is known and is disclosed, for example, by German Patent No. 41 21 586 A1, FIGS. 3 and 4. On account of the arrangement of the plate which is non-rotationally fastened to the turbine wheel between the piston and the converter housing, the number of friction surfaces is twice as high as in torque converters without this plate, which means that higher torques can be transmitted by means of the lock-up clutch. But while the piston, with its side facing the turbine wheel, is exposed to cooling oil, there is a risk that the converter housing, in the longitudinal area of the corresponding friction lining, will overheat on account of the insufficient access of an oil stream to the corresponding point of the converter housing, and will thereby be damaged. The risk of overheating occurs in particular if the converter housing and piston are deliberately moved with slip in relation to the corresponding friction lining to damp any vibrations which may occur.
European Patent No. 0 428 248 A2 discloses a known torque converter which has only one friction surface between the piston and the converter housing, in which this friction surface is designed with channels for the passage of oil, so that the oil can remove the heat which is generated when the piston is operated with a predetermined slip in relation to the converter housing. The channels are designed along the entire circumference of the friction lining, and run radially outward, starting from a connection opening to the converter circuit.
On the torque converter described immediately above, the piston, being disposed with respect to the converter housing, is also exposed to cooling oil, on its side facing away from the friction lining, so that on account of the presence of the channels carrying the oil flow in the friction lining, the temperatures on the piston and the converter housing can of course be reduced, but there remains an undesirable temperature difference between the two converter elements. An insufficiently strong oil flow in the channels would consequently lead to an overheating of the converter housing in the vicinity of the friction lining.